EP1255774B1

EP1255774B1 - Methods for identifying compounds useful for the treatment of obesity involving foxc2

Info

Publication number: EP1255774B1
Application number: EP01904775A
Authority: EP
Inventors: Sven Enerbäck; Peter Carlsson
Original assignee: LeanGene AB
Current assignee: LeanGene AB
Priority date: 2000-02-18
Filing date: 2001-02-16
Publication date: 2005-09-14
Anticipated expiration: 2021-02-16
Also published as: JP2003523192A; WO2001060853A1; AU3259901A; IS6502A; CA2400342A1; IL150951A0; ATE304552T1; AU2001232599B2; DE60113380D1; NO20023709L; DE60113380T2; NZ521005A; EP1255774A1; NO20023709D0

Abstract

According to the invention, a major role for the winged helix protein FOXC2 in regulating energy balance and adiposity is demonstrated. The invention relates to transgenic non-human mammalian animals being capable of expressing the human FOXC2 gene in its adipose tissue. The invention also relates to methods for identifying compounds useful for the treatment of medical conditions related to obesity or diabetes, said compounds being capable of stimulating expression of the human FOXC2 gene, or being capable of stimulating the biological activity of a polypeptide encoded by the human FOXC2 gene. The invention further relates to methods for identifying compounds useful for the treatment of medical conditions related to malnutrition, said compounds being capable of decreasing expression of the human FOXC2 gene, or being capable of decreasing the biological activity of a polypeptide encoded by the human FOXC2 gene.

Description

TECHNICAL FIELD

The invention relates to transgenic non-human mammalian animals being capable of expressing the human FOXC2 gene in its adipose tissue. The invention also relates to methods for identifying compounds useful for the treatment of medical conditions related to obesity or diabetes, said compounds being capable of stimulating expression of the human FOXC2 gene, or being capable of stimulating the biological activity of a polypeptide encoded by the human FOXC2 gene. The invention further relates to methods for identifying compounds useful for the treatment of medical conditions related to malnutrition, said compounds being capable of decreasing expression of the human FOXC2 gene, or being capable of decreasing the biological activity of a polypeptide encoded by the human FOXC2 gene.

BACKGROUND ART

More than half of the men and women in the United States, 30 years of age and older, are now considered overweight, and nearly one-quarter are clinically obese (Wickelgren, 1998). This high prevalence has led to increases in the medical conditions that often accompany obesity, especially non-insulin dependent diabetes mellitus (NIDDM), hypertension, cardiovascular disorders, and certain cancers. Perhaps most importantly, obesity confers a significant increased rate of mortality when compared with that of individuals of normal body weight. Obesity results from a chronic imbalance between energy intake (feeding) and energy expenditure. Energy expenditure has several major components including basal metabolism, physical activity, and adaptive (nonshivering) thermogenesis. This latter process refers to energy that is dissipated in response to changing environmental conditions, most notably exposure to cold or excessive caloric intake (so-called diet-induced thermogenesis). To better understand the mechanisms that lead to obesity and to develop strategies in certain patient populations to control obesity, we need to develop a better underlying knowledge of the molecular events that regulate the differentiation of preadipocytes and stem cells to adipocytes, the major component of adipose tissue.

Role of adipose tissue

The reason for existence of the adipocyte is to store energy for use during periods of caloric insufficiency. Postprandially, dietary fat is absorbed via the intestine and secreted into the circulation as large triglyceride (TG) rich particles called chylomicrons (chylo). Lipoprotein lipase (LPL), although produced by adipocytes, is localized to the endothelial cell surface where it hydrolyses TG resulting in the release of free fatty acids (FFA). Much of these are taken up by the adipose tissue either passive or active via FFA transporters. The FFAs are then activated to an acyl CoA form and re-esterified by an enzymatic cascade to form storage TG. At the same time, glucose, which also increases in the circulation postprandially, is taken up into adipose tissue via specific plasma membrane glucose transporters. These two substrates (glucose and FFA) are the building blocks for formation of storage TG. On the other hand, during fasting, FFAs are released from the adipose tissue TG pool through the action of hormone sensitive lipase (HSL: Fig. 1). Clearly, efficient functioning of adipose tissue is dependent on the coordinated control of each of these processes and the proteins involved.
In recent years, a growing body of evidence has demonstrated a dual role for adipocytes, also being a source of numerous hormones that regulate both the adipocyte itself and many other systems within the body. Adipocytes produce leptin as a function of adipose energy stores. Leptin acts through receptors in the hypothalamus to regulate appetite, activity of brown adipose tissue (BAT), insulin secretion via sympathetic nervous system output, and important neuroendocrine adaptive responses to fasting and control of reproduction. The gene encoding leptin was identified by positional cloning (Zhang et al., 1994) and is the mutation leading to the profound obese phenotype of the ob/ob mouse, characterized by severe obesity, NIDDM, diminished fertility and hypothermia. The db-gene codes for a hypothalamic receptor for leptin (Chua et al., 1996) and the db/db mutant mice show a similar phenotype with ob/ob mice, but here the defect lies in the block of leptin receptor downstream signaling. After leptin administration, it was possible to correct the defect only in the ob/ob, but not db/db mice as predicted by Coleman's parabiosis experiments (Coleman, 1973).
Another adipocyte product, the cytokine tumor necrosis factor α (TNFα), has profound effects on adipocyte differentiation, and energy metabolism, and can even induce adipocyte dedifferentiation and apoptosis. Furthermore, TNFα has more systemic implications as it has been shown to play a role in the genesis of insulin resistance associated with obesity (Hotamisligil et al., 1993). In obese humans and numerous rodent models of obesity-diabetes syndromes, there is a marked elevation in muscle and adipose TNFα production, as compared with tissues from lean individuals (Hotamisligil et al., 1995; Hotamisligil et al., 1993). TNFα levels can be reduced with weight loss (Hotamisligil et al., 1995) or after treatment with the insulin-sensitizing agent pioglitazone (Nofmann et al., 1994).
A third adipocyte product, the acylation stimulating protein (ASP) exert autocrine action on the adipocyte, having potent anabolic effects on human adipose tissue by stimulation of glucose transport and FFA esterfication (Maslowska et al., 1997; Walsh et al., 1989). ASP is generated by the interaction of complement D (identical to adipsin), factor B, and complement C3, components of the alternate complement pathway all produced by adipocytes (Choy and Spiegelman, 1996).

White adipose tissue versus brown adipose tissue

There are two different types of adipose tissue in the body, WAT and BAT, which have quite opposite physiological functions although they both have the same "machinery" for lipogenic and lipolytic activity. WAT stores excess energy as triglycerides and releases free fatty acids in response to energy requirements at other sites. BAT on the other hand is involved in adaptive (non-shivering) thermogenesis. BAT is found only at certain sites in the body of rodent, such as in interscapular, perirenal and retroperitoneal regions. In human neonates BAT is present in large quantities but its thermogenic activity decreases shortly after birth and the tissue is gradually converted into white type adipose tissue (Lean et al., 1986). However, judged by expression of the brown fat specific uncoupling protein 1 (UCP1) mRNA, substantial amounts of brown adipocytes exist throughout life in human adipose deposits, which are generally classified as white (Krief et al., 1993).
Brown adipocytes have a multilocular disposition of fat droplets, i.e. a number of individual droplets within each adipocyte, whereas the white adipocyte has a single fat droplet within the cell. Furthermore, the brown adipocyte has a central nucleus and a large number of mitochondria in contrast to the white adipocyte, which has very few mitochondria and a nucleus that is displaced towards the plasma membrane by the lipid droplet. The only known gene marker to distinguish BAT from WAT, or any other celltypcs is the expression of UCPI in brown adipocytes. Due to the presence of this unique mitochondrial protein brown adipocytes have the ability of facultative heat production, which is highly regulated by sympathetic nerve activity. UCP1 is a proton translocator in the inner mitochondrial membrane and functions as a facultative uncoupler of the mitochondrial respiratory chain (Nicholls and Locke, 1984). Recently two new uncoupling proteins have been identified and cloned through their sequence homology with UCP1. UCP2 is found in most tissues (Fleury et al., 1997), while UCP3 is expressed in BAT and skeletal muscle (Boss et al., 1997). The respective roles for UCP2 and UCP3 in thermogenesis and energy balance of intact animals remain to be determined. That brown fat is highly important in rodents for maintaining nutritional homeostasis is predicted by the facts that the function of BAT is impaired in obese rodents (Himms-Hagen, 1989) and transgenic mice with decreased brown fat mass develop obesity (Lowell et al., 1993). Since BAT is much less obvious in large animals like humans, than in rodents, skeletal muscle is thought to be the site of primary importance for normally occurring adaptive thermogenesis in large animals.
Both white and brown fat are innervated under the control of the sympathetic nervous system. There are at least three pharmacologically distinct subtypes of β-adrenergic receptors (β₁, β₂, and β₃) found in adipocytes. The β₃-adrenergic receptor (β₃-AR) is the predominant subtype in adipose tissue and it mediates the effects of norepinephrine present in the sympathetic synaptic cleft during nerve stimulation of lipolysis in WAT and BAT and of thermogenesis in BAT (Giacobino, 1995). Increased lipolysis takes place primarily through the production of cAMP and the activation of hormone-sensitive lipase through phosphorylation (Fig. 1). Thermogenesis in BAT is accomplished by increased UCP1 mRNA levels through stimulation of transcription (Rehnmark et al., 1990; Ricquier et al., 1986). Uncoupled respiration is also thought to be stimulated by increased lipolysis and the raise in intracellular concentration of FFA (Jezek et al., 1994). Sympathetic stimulation of brown fat also contributes to regulation of energy expenditure by increasing mitochondrial biogenesis (Wu et al., 1999a) and hyperplasia of brown adipocytes. In rodents, β₃-adrenergic receptors (β₃-ARs) are abundant in WAT and BAT (Granneman et al., 1991; Muzzin et al., 1991; Nahmias et al., 1991), white in humans, β₃-AR mRNA is abundant in BAT only, with much less or no β₃-AR mRNA found in WAT (Granneman and Lahners, 1994; Krief et al., 1993). Long-term treatment of obese rodents with β₃-selective agonists reduces fat stores and improves obesity-induced insulin resistance (Bloom et al., 1992; Cawthorne et al., 1992: Holloway et al., 1992). Thus, β₃-selective agonists are promising anti-obesity compounds. Trials of β₃-AR agonist treatment, aimed at stimulating BAT in humans have proved disappointing with respect to weight loss (Arch and Wilson, 1996). The true potential of β₃-AR agonists in humans can only be evaluated when a compound with good selectivity and efficacy at the human β₃-AR, coupled with a long duration of action in vivo, has been identified, however those compounds that have been evaluated in humans so far have much lower efficacy at the human than the rodent receptor. This could be explained by the fact that human and mouse/rat β₃-AR show a ~80% similarity in their amino acid sequence. Several of the β₃-AR-selective agonists (e.g. BRL 37344 and CL 316,243) have been shown to he extremely potent against mouse and rat β₃-AR but with a greatly reduced activity against the human β₃-AR. Presently, recombinant cell lines expressing human β₃-ARs are being used to identify compounds with an increased potency against the human receptor (Ito et al., 1998). Mice with targeted mutagenesis of the β₃-AR gene show only a modest tendency to become obese and their brown fat response to cold exposure works perfectly normal (Susulic et al., 1995). Deficient mice displayed an up-regulation of β₁-AR mRNA levels in both white and brown fat which most probably is the reason of the mild phenotype. These results implicate that it is possible that β₁- and β₂-ARs also play important roles in innervation of adipose tissue. Moreover, other species, including humans, have higher levels of β₁-and β₂-ARs, then β₃-AR, in adipose tissue (Lafontan and Berlan, 1993).

Adipocyte differentiation

There has been some great progress during the past few years in the understanding of the adipocyte differentiation program. Most of the work leading to this understanding has been carried out using white preadipose cell lines in culture, notably the C3H10T½ and NIH 3T3 fibroblastic cell lines and the 3T3-L1 and 3T3-F442A preadipocyte cell lines. Treatment of multipotent C3H10T½ cells with 5-azacytidine (a demethylating agent) gives rise to cells committed to the myogenic, adipogenic, osteoblastic, or chondrogenic lineages. This is consistent with the view that the adipose lineage arises from the same multipotent stem cell population of mesodermal origin that gives rise to the muscle and cartilage lineages (Cornelius et al., 1994). Under appropriate hormonal control (e.g. glucocorticoid, insulin-like growth factor-1, and cyclic AMP or factors that mimic these agents) or experimental manipulation white preadipose cell lines are capable to differentiate into mature white adipocytes (Ailhaud et al., 1992). Several transcription factors have been identified, which act co-operatively and sequentially to trigger the functional differentiation program (Fig. 2).

Transcriptional control of adipocyte differentiation through PPARs C/EBPs, and ADD1/SREBP1

Peroxisome proliferator-activated receptors (PPARs) are a class of the nuclear hormone receptors. The member PPARγ is now well recognized as serving an important role in the regulation of adipogenesis. Through the use of alternate promoters, the gene encoding PPARγ gives rise to two separate products, PPARγ1 and PPARγ2, the latter containing an additional 28 N-terminal amino acids that are reported to enhance ligand binding (Fajas et al., 1997; Werman et al., 1997). Reports that ligand activation of retrovirally expressed PPARγ2 in non-differentiating NIH-3T3 cells potently promoted adipocyte differentiation provided the most compelling evidence for the adipogenic nature of PPARγ2 (Tontonoz et al., 1994b). One live-born PPARγ deficient mouse has been produced and it displayed a total absence of WAT and BAT (complete lipodystrophy) and fatty liver, secondary to lipodystrophy (Barak et al., 1999).
Members of the PPAR family specifically function as heterodimers with the retinoid X receptor (RXR) through interactions with peroxisome proliferator response elements (PPREs) on target genes, including lipoprotein lipase (LPL; Schoonjans et al., 1996), the adipocyte fatty acid-binding protein 422/aP2 (Tontonoz et al., 1994a), phosphoenolpyruvate carboxykinase (PEPCK; Tontonoz et al., 1995), and stearocyl-CoA desaturase I (Miller and Ntambi, 1996). Transcriptional activity of PPARγ is induced following binding of either synthetic or naturally occurring ligands, including prostaglandins of the D2 and J2 series, with the 15-deoxy-Δ 12, 14-prostaglandin J2 derivate emerging as one of the most potent (Forman et al., 1995). Synthetic ligands that activate PPARγ include carbacyclin and a new class of antidiabetic drugs, the thiazolidinediones (TZDs) (Lehmann et al., 1995). TZDs promote adipogenesis in culture and improve insulin sensitivity in vivo. PPARγ activators probably modify the production of adipocyte-derived mediators of insulin resistance, such as free fatty acids or TNFα. PPARγ activation will decrease production of TNFα by adipocytes and interfere with its inhibitory effect on insulin signaling (Peraldi et al., 1997).
In addition, because of its tissue selective effects on genes involved in fatty acid uptake, PPARγ activation will induce repartitioning of fatty acids in the body, with enhanced accumulation of fatty acids in adipose tissue at the expense of a relative depletion of muscle fatty acids (Martin et al., 1997). The relative lipid depletion of muscle cells will improve their glucose metabolism and result in an improvement in insulin sensitivity. Furthermore, PPARγ decreases the expression of the adipocyte-derived signaling molecule leptin, which results in an increase in energy intake and optimization of energy usage, contributing further to PPARγ's adipogenic effect (De Vos et al., 1996). Recently it has been demonstrated that interaction with a novel cofactor PPARγ coactivator (PGC-1), could enhance PPARγ transcriptional activity in brown adipose tissue (Puiaserver et al., 1998).
Three members of the CCAAT/enhancer-binding protein (C/EBP) family of transcription factors, i.e. C/EBPα, C/EBPβ, and C/EBPδ, have been implicated in the induction of adipocyte differentiation. The factors are proteins of the bZIP class, with a basic domain that mediates DNA binding and a leucine zipper dimerization domain. Cyclic AMP and adipogenic hormones such as glucocorticoids and insulin induce a transient increase in the expression of C/EBPβ and δ early in adipocyte differentiation (Cao et al., 1991; MacDougald et al., 1994; Yeh et al., 1995). C/EBPβ, in synergy with C/EBPδ, then induces PPARγ expression in the preadipocyte (Wu et al., 1996, Wu et al., 1995). Mice lacking the C/EBPβ, and C/EBPδ gene have normal expression of C/EBPα and PPARγ, but this co-expression of C/EBPα and PPARγ is not sufficient for complete adipocyte differentiation in the absence of C/EBPβ and C/EBPδ (Tanaka et al., 1997). C/EBPα seems to play an important part in the later stages of differentiation by maintaining the differentiated adipocyte phenotype through autoactivation of its own gene (Lin and Lane, 1992; Lin and Lane, 1994). C/EBPα activates several adipocyte-specific genes such as the insulin-responsive glucose transporter-4 (GLUT4) (Kaestner et al., 1990). 422/aP2 (Christy el al., 1989), UCP (Yubero et al., 1994), and also the insulin receptor gene, and insulin receptor substrate I (IRS-1) (Wu el al., 1999b). Definitive proof that C/EBPα is required for adipocyte differentiation was obtained by showing that expression of antisense C/EBPα RNA in 3T3-L1 preadipocytes prevented differentiation (Samuelsson et al., 1991). Consistent with this finding, disruption of the C/EBPα gene gave rise to mice that failed to develop white adipose tissue (Wang el al., 1995). Taken together these findings proved that C/EBPα is both required and sufficient to induce adipocyte differentiation. The expression of C/EBPα, as well as other adipocyte genes, is induced upon ligand activation of PPARγ. Through a positive feedback loop, C/EBPα maintains the expression of PPARγ. C/EBPα and PPARγ cooperate to promote adipocyte differentiation, including adipocyte gene expression and insulin sensitivity (Wu et al., 1999b). It is possible that C/EBPα is ultimately an important, indirect target of the antidiabetic actions of the TZDs.
ADD1/SREBP1 (adipocyte determination and differentiation-dependent factor l/sterol regulatory element binding protein 1) is a member of the basic helix-loop-helix (bHLH) class of transcription factors. In the inactive state, the protein is membrane-bound to the endoplasmic reticulum. Upon activation (such as a low cholesterol state), ADD1/SREBP1 is proteolytically cleaved and the soluble form becomes translocated to the nucleus where it binds one of two different response elements, namely the E box and the sterol regulatory element (SRE; Brown and Goldstein, 1997). The expression of ADD1/SREBP1 is induced during differentiation of adipocytes, where it activates transcription of target genes involved in both cholesterol metabolism and fatty acid metabolism (Kim and Spiegelman, 1996). ADD1/SREBP1 potentiates the transcriptional activity of PPARγ probably through the production of endogenous ligands for PPARγ (Kim et al., 1998) and also by binding to and inducing the PPARγ promoter (Fajas et al., 1999).
When preadipocytes differentiate into adipocytes, several differentiation-linked genes are activated. Lipoprotein lipase (LPL) is one of the first genes induced during this process (Fig. 2). Two cis-regulatory elements important for gradual activation of the LPL gene during adipocyte development in vitro have been delimited (Enerback et al., 1992). These elements, LP-α and LP-β, contained a striking similarity to a consensus sequence known to bind transcription factors of the winged helix family. Results of gel mobility shift assays and DNase I and exonuclease III in vitro protection assays indicated that factors with DNA-binding properties similar to those of the winged helix family of transcription factors are present in adipocytes and interact with LP-α and LP-β. There is a need for identifying human winged helix genes that could be responsible for the induction of the LPL promoter and possibly regulating expression of other adipocyte specific genes.

"Fork head" and "winged helix" genes

The "fork head" domain is an evolutionary conserved DNA-binding domain of 100 amino acids, which emerged from a sequence comparison of the transcription factor HNF-3α of rat and the homeotic gene fork head of Drosophila. X-ray crystallography of the fork head domain from HNF-3γ revealed a three-dimensional structure, the "winged helix", in which two loops (wings) are connected on the C-terminal side of the helix-loop-helix (for reviews, see Brennan, R.G. (1993) Cell 74, 773-776; Lai, E. et al. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 10421-10423).
The isolation of the mouse mesenchyme forkhead-1 (MFH-1) and the corresponding human (FKHL14) chromosomal genes is disclosed by Miura, N. et al. (1993) FEBS letters 326: 171-176; and (1997) Genomics 41: 489-492. The nucleotide sequences of the mouse MFH-1 gene and the human FKHL14 gene have been deposited with the EMBL/GenBank Data Libraries under accession Nos. Y08222 (SEQ ID NO: 5) and Y08223 (SEQ ID NO: 8), respectively. A corresponding gene has been identified in Gallus gallus (GenBank accession numbers U37273 and U95823).
The International Patent Application WO 98/54216 discloses a gene encoding a Forkhead-Related Activator (FREAC)-11 (also known as S12), which is identical with the polypeptide encoded by the human FKHL14 gene disclosed by Miura, supra.
The nomenclature for the winged helix / forkhead transcription factors has been standardized and Fox (Forkhead Box) has been adopted as the unified symbol (Kaestner et al. (2000) Genes & Development 14: 142-146; see also htpp://www.biology.pomona.edu/fox). It has been agreed that the genes previously designated MFH-1 and FKHL14 (as well as FREAC-11 and S 12) should be designated FOXC2.

DESCRIPTION OF THE DRAWINGS

FIGURE 1

Schematic view of lipogenic and lipolytic actions in the adipocyte. Triglycerides are hydrolyzed to glycerol and free fatty acids by the action of lipoprotein lipase. FFAs are transported into the adipocyte via FATP. FFAs are combined with acetyl CoA to produce acyl CoA, which is re-esterfied to triglycerides. The multi-enzyme complex hormone sensitive lipase hydrolyses triglycerides into FFAs and glycerol. FFAs can either be re-esterfied again or be released into the circulation. LPL, lipoprotein lipase; FFA, free fatty acid: FATP, fatty acid transport protein; aP2, adipocyte fatty acid-binding protein 422/aP2; ACS, acyl CoA synthetase; Glut4, glucose transporter IV; βAR, β-adrenergic receptor; AC, adenylate cyclase; PKA, protein kinase A; HSL, hormone sensitive lipase. Figure is adapted from Sethi and Hotamisligil, 1999.

FIGURE 2

Summary of different stages and events during in vitro adipocyte differentiation. Our current understanding of adipocyte differentiation indicates that a pluripotent stem cell precursor gives rise to a mesenchymal precursor cell (multipotent) with the potential to differentiate along mesoderma linages of myoblast, chondroblast, osteoblast, and adipocyte. Given appropriate environmental and gene expression cues, preadipocytes undergo clonal expansion and subsequent terminal differentiation. Selected molecular events accompanying this process are indicated above. Pref-1, preadipocyte factor 1; pOb24/A2COL6, α2 chain of type VI collagen; LPL, lipoprotein lipase; aP2, adipocyte fatty acid-binding protein 422/aP2; UCP, uncoupling protein; CUP, C/EBPα undifferentiated protein; FAAR, fatty acid-activated receptor; PPARγ, peroxisome proliferator-activated receptor γ; C/EBP, CCAAT/enhancer binding protein; RXR, retinoid X receptor. Figure is adapted from Klaus, 1997.

FIGURE 3

Northern blot analysis. Adult human tissues (a) and wt adult mouse tissues (b). The blots were analysed with probes specific (with no cross-reactivity) for FOXC2 (human) and FoxC2 (mouse), respectively. The experiments were carried out with 20 µg of total RNA/lane using β-actin as an internal control. Mouse adipose tissue (c) was treated with collagenase (see under "Methods"), RNA from the adipocyte fraction (Adip F) and the stroma/vascular fraction (SVF) were used and probed for FoxC2, LPL and GAPDH (control). In (d) 3T3-LI cells were differentiated to adipocytes in culture and then incubated for 6 hours in the absence (Basal) or presence of forskolin (Forsk.; 100 µM), 12-O-tetradecanoylphorbol-13-acetat (TPA; 100 nM), Ca²⁺ ionophore (A23187; 0.5 µM) alone or in combination as indicated. Northern blot analysis was performed and the FOXC2 mRNA signal was assessed by β-scintillation counting in a dot-matrix β-counter. Image shows counts over the filter plotted in gray-scale intensity. Bars above the Northern blot represent actual cpm over mean cpm of controls subtracted of background cpm given as "fold induction".

FIGURE 4

Schematic view of FOXC2 transgene construct and Southern blot detection of integration positive mice. A 2.1-kb fragment containing the FOXC2 cDNA was ligated downstream of the 5.4-kb aP2 enhancer/promoter region (A). Prior to pronuclear injection the transgene construct was liberated from the plasmid as an 8.9-kb NotI/AgeI fragment. A 1.7-kb fragment of the aP2 promoter was used as a probe in Southern blot analysis for identification of integration positive mice. Panel B shows the identification of the three founders investigated further.

FIGURE 5

(a): Weights of intra-abdominal WAT and interscapular BAT depots from tg mice (founder lines Tg-A. Tg-B and Tg-C) compared to that of wt mice. (b): Ratios between weights of intra-abdominal WAT to interscapular BAT for wt and tg founder lines A, B and C. Values are means ±SEM. n=4 in each group. (c): Expression levels of the FOXC2 transgene in white adipose tissue (WAT) and brown adipose tissue (BAT) of wild-type mice (WT) and FOXC2 transgenic mice (founder A, B, and C) as measured by Northern blot analysis (12 µg of total RNA/lane). GAPDH was used as a control.

FIGURE 6

A 5-months-old wild-type female and a FOXC2 transgenic female littermate. A, C, and E show WT: B. D. and F show transgenic littermate. (A, B) An exposed dorsal view of the interscapular brown fat pads, illustrating an increased size of the depot in the transgenic mouse. (C. D) An exposed ventral view, illustrating a reduction in size and change in appearance of the intrabdominal white fat pads in the transgenic mouse. (E, F) The interscapular brown fat pads and the intrabdominal white fat pads have been dissected out. BAT at the top and WAT at the bottom.

FIGURE 7

Histologic sections of brown fat (A, B), and white fat (C, D) from a 5-months-old wild-type mouse (left) and a FOXC2 transgenic littermate (founder A) (right). (A, B) Interscapular brown fat of the transgenic mouse consists of markedly enlarged adipocytes containing large unilocular fat droplets. (C, D) Adipocytes in white fat of the transgenic mouse show heterogeneity of size. This is in contrast to the WAT from a wild-type mouse. which consists of adipocytes of uniform size filled with a large. unilocular vacuole. In a cold adaptation experiment, mice were kept at either room temperature (RT) or at 4°C for 24 hours. Whereas there is no apparent difference between BAT from wt mice (E, G), the number and size of lipid droplets present in tg BAT at room temperature is clearly reduced when exposed to 4°C (F, H). Scale bar depicted in G equals 100 µm.

FIGURE 8

Change of size of fat depots in FOXC2 transgenic mice (founder C). (A) Weight comparison (expressed as percent of total body weight) for intrabdominal fat depots and interscapular brown fat depots of 5-months-old wild-type females and FOXC2 transgenic littermates. Changes are significant, P<0.005. (B) Ratio between weights of the intrabdominal fat depot and the interscapular brown fat depot. Change is significant, P<0.0005. (C) No significant difference in body weight could be detected between the two groups. (D) No significant difference in food consumption was noticed when measured during a time period of two months. Data are means ±SD, n=3 for both WT and founder C in A-C, n=4 for both WT and founder C in D.

FIGURE 9

Amount of different mRNAs in white adipose tissue (WAT) and brown adipose tissue (BAT) of wild-type mice (WT) and FOXC2 transgenic mice (founder A, B, and C) as measured by Northern blot analysis (12 µg of total RNA/lane). GAPDH was used as a control for ensuring equal loading on all blots.

FIGURE 10

Serum triglyceride is lowered in FOXC2 transgenic mice (founder A). Serum triglyceride content was analyzed for 14-weeks-otd wild-type males and FOXC2 transgenic littermates fed ad libitum. Change is significant, P<0.005. Data are means ±SD, n=4 for both WT and founder A.

FIGURE 11

Total body lipid content is lowered in FOXC2 transgenic mice (founder A). Total body lipid content was analyzed for 6-months-old wild-type males and FOXC2 transgenic littermates fed ad libitum. Change is significant, P<0.0005. Data are means ±SD; WT, n=3 and founder A, n=4.

FIGURE 12

Blood glucose is lowered (A) and glucose elimination is more efficient (B) in FOXC2 transgenic mice (founder A). (A) Blood glucose levels were analyzed for 10-weeks-old wild-type mice and FOXC2 transgenic littermates fed ad libitum. A significant (P<0.05) reduction of blood glucose levels were seen for FOXC2 transgenic mice. (B) An intravenous glucose tolerance test was carried out on the mice used in (A). Blood samples were taken immediately before and at 1,5,20, and 50 min after intravenous injection of glucose (1 g/kg). The values were significantly changed at 0 min (P<0.05), 20 min (P<0.001), and at 50 min (P<0.05). Data are means ±SD; n=10 for both WT and founder A.

FIGURE 13

Plasma insulin is lowered in FOXC2 transgenic mice (A), still levels raised higher than in wild-type after intravenous (iv) glucose load (B, C) (founder A). (A) Plasma insulin levels were analyzed for 10-weeks-old wild-type mice and FOXC2 transgenic littermates fed ad libitum. A significant (P<0.05) reduction of plasma insulin levels was seen for FOXC2 transgenic mice. (B) An intravenous glucose tolerance test was carried out on the mice used in (A) Blood samples were taken immediately before and at 1, 5, 20. and 50 min after intravenous injection of glucose (1 g/kg). The values were significantly changed at 0 min (P<0.05), 20 min (P<0.01), and at 50 min (P<0.05). (C) Fold induction of plasma insulin levels one minute after i.v, glucose load. Change is significant, P<0.005. Data are means ±SD; n=10 for both WT and founder A.

FIGURE 14

Hypothetical action of FOXC2 in adipocytes. Filled arrow indicates known positive transcriptional regulation. Open arrow represents a proposed action of FKHL14. ADD1/SREBP1 both activates transcription of acetyl CoA carboxylase (Lopez et al., 1996), fatty acid synthase (FAS), and lipoprotein lipase (LPL), and increases the transcriptional activity of PPARγ (Fajas et al., 1999). PPARγ activates transcription of fatty acid transport protein (FATP), acyl-CoA synthetase genes (ACS: Martin et al., 1997), adipocyte fatty acid-binding protein 422/aP2 (aP2; Tontonoz et al., 1994a), LPL (Schoonjans et al., 1996), and phosphoenolpyruvate carboxykinase (PEPCK; Tontonoz et al., 1995). C/EBPα activates insulin-responsive glucose transporter-4 (GLUT4; Kaestner et al., 1990), aP2 (Christy et al., 1989), uncoupling protein I (UCP1; Yubero et al., 1994), the insulin receptor (InsR), insulin receptor substrate-1 (IRS-1; Wu et al., 1999b), and PEPCK (Park et al., 1990). A positive feedback loop between C/EBPα and PPARγ have been suggested (Wu et al., 1999b).

FIGURE 15

Reduction in weight gain in (transgenic) tg mice. Analysis were performed on tg-A mice with wt littermates as controls, fed ad libitum, mice were approximately 4-6 months of age. There is a reduction in diet induced weight gains in FOXC2tg mice, both in females (p<0.02; a) and males (p<0.03; b), as compared with wt mice, values are means ±SEM, n=4 in each group. Mice were on a high fat diet (58.0% on a caloric basis) for seven weeks (see Methods).

FIGURE 16

Metabolic profile. Analysis were performed on tg-A mice with wt littermates as controls, mice were approximately 4-6 months of age and fed ad libitum, values are means ±SEM. a, Total body lipid content was analysed as total lipid content of carcasses (see Methods), n=4 in each group, p<0.0004. b, Serum triglyceride is lowered in FOXC2tg mice, n=4 in each group, p<0.004. c, Serum cholesterol, no significant difference between wt and tg mice, n=4 in each group, d, Plasma free fatty acids (FFA) is lowered in tg mice as compared with wt littermates, n=4 in each group, p<0.02. e, Non-fasting plasma glucose is lowered in FOXC2 tg mice, n=20 in each group, p<0.01. f, Plasma insulin is lowered in tg mice, analysis was performed on the same animals as in e, p<0.001. There is a reduction in diet induced weight gains in FOXC2tg (n=7) mice as compared with wt (n=9; p<0.01; g). Whereas the body lipid content after a high fat diet (h) increases for both wt and tg mice, as compared with mice on a standard diet (a), we note a reduction for tg (n=4) mice as compared with wt (n=6; p<0.0001) in h. The weight gain to grams of eaten food ratio was calculated for wt (n=10) and tg (n=9) mice on a control diet (i), no significant differences could be detected. In the corresponding experiment, with mice on a high fat diet, there is a 30% reduction (p<0.01) for tg (n=7) as compared wt (n=9) mice (i). No gender differences were observed.

FIGURE 17

Intravenous glucose tolerance test. Wt and tg-A mice were fed a control (a, b) or high fat (c, d) diet for 14 weeks (for details see under "Methods"). After intravenous (i.v.) injection of glucose (1 g/kg), blood samples were drawn immediately before and at 1, 5, 20, 50 and 75min. Plasma glucose levels differ significantly between wt and tg mice both on a control (a, tg n=8, wt n=9; p<0.02) as well as on a high fat diet (c, tg=5, wt=6; p<0.001). Plasma insulin values differ also significantly between wt and tg mice both on a control diet (b, p<0.001) and a high fat diet (d, p<0.001). Values are means ±SEM, no gender differences were observed.

FIGURE 18

Altered β-adrenergic sensitivity, PKA isozyme composition and activation kinetics in adipose tissue from FOXC2 tg-A mice. (a) Left panel: CAT reporter activity directed from the RIα promoter transfected together with FOXC2 expression vector or control vector into 3T3-L 1 pre-adipocytes. Data (n=3 experiments) are CAT values normalised for transfection efficiency, expressed as fold induction. Right panel: RIα and GAPDH mRNA levels in WAT from wild type (wt) and the three founder strains (A, B. C) over-expressing FOXC2. (b) Levels of RIα and RIIβ immunoreactive protein in WAT and BAT from transgenic animals (n=4) compared to wild type litter mates (expressed relative to wild type levels). (c) Kinase activities using Kemptide as substrate in the presence (total. open bars) or absence (free, solid bars) of 5 µM cAMP. Activities in transgenic WAT and BAT (n=4) are shown relative to those in wild type litter mates. (d) Kinase activities towards Kemptide measured in WAT homogenates from transgenic and wild type littermate mice incubated with increasing concentrations of cAMP. Data are representative of 2 pairs of animals analysed. Total cAMP-inducible activity was set to 100%. Right panel, immunoblot demonstrating WAT levels of RIα and RIIβ. Intracellular cAMP levels in adipocyte suspensions prepared from WAT of transgenic animals and wild type littermates (each pooled from 3 animals) and stimulated with either (e) a non-selective β-agonist (isoproterenol, I µM) or (f) a β3-selective agonist (CGP-12177A, 1 µM). Equal amounts of cells were withdrawn at different time points (0 to 10 min), mixed with stop buffer and flash-frozen. Mean ± half range (SEM) of duplicate determinations are shown.

DISCLOSURE OF THE INVENTION

According to the present invention, the human transcription factor gene FOXC2 is identified as a key regulator of adipocyte metabolism. Increased FOXC2 expression, in white (WAT) and brown adipose tissue (BAT), has a pleiotropic effect on gene expression, which leads to resistance to diet induced weight gain and a decrease in: total body lipid content, serum triglycerides, plasma levels of free fatty acids, glucose and insulin. To our knowledge, FOXC2 is the hitherto only identified gene that, in a concerted action, can counteract most, if not all, of the symptoms associated with obesity, including hypertriglyceridemia and insulin resistance; a likely consequence hereof would be protection against type 2 diabetes.
During adulthood, the human winged helix gene FOXC2 is expressed exclusively in adipose tissue. The LPL mRNA levels in the FOXC2 transgenic mice seem to be slightly elevated (Fig. 9), which is in concordance with the initial findings that the two winged helix cis-regulatory elements are responsible for the inducibility of the LPL promoter (Enerback et al., 1992). The higher expression level of LPL most probably is responsible for the significantly decreased plasma TG levels noticed in FOXC2 transgenic mice (Fig. 10), in addition to the fact that the profound up-regulation of adipsin in both WAT and BAT (Fig. 9) most certainly is of great importance. Adipsin is a secreted protein necessary for the formation of acylation stimulating protein (ASP), which has potent anabolic effects on human adipose tissue for both glucose and free fatty acid (FFA) storage (Cianflone et al., 1995).
The extensive alternations seen in the FOXC2 transgenic mice presented here predicts a very central and important role for this winged helix gene hitherto unknown to participate in molecular events in adipose tissue. It has been demonstrated by gene targeting experiments that the mouse homologue, Mfh1, plays a crucial role during embryonic development (Iida et al., 1997; Winnier et al., 1997), but so far nothing has been published about its function in adult mice. In a recent publication an Mfh1/Pax1 double mutant was shown to be totally absent of BAT at day 15.5 dpc (Furumoto et al., 1999).
The FOXC2 transgenic mice had a clear reduction in white adipose tissue mass. The reduced size of the white fat depots might be due solely to the reduction in size of the adipocytes (Fig. 7), but one cannot rule out the possibility that there is also a reduction in adipocyte number. There are a number of possible reasons why the FOXC2 transgenic mice have decreased size of white adipocytes. One might presume an increased lipolytic activity of their adipocytes in general; coupled with the greater mass of brown fat this may lead to increased energy expenditure through heat production by BAT giving rise to the lean phenotype. The upregulation of β₃-AR seen in transgenic WAT (Fig. 9) will result in an elevated activation of HSL hence an increase in lipolysis (Fig. 1) ultimately leading to reduced lipid storing.
Furthermore, the transgenic mice were insulin sensitive (Fig. 13); this could be explained by both the upregulation of genes involved in insulin action (lnsR, IRS-I, IRS-2, and GLUT4; Fig. 9) and the lean body composition (Fig. 11). Insulin has a critical role in lipid metabolism, promoting the storage of triglycerides in adipocytes through numerous actions on this cell. Among these are stimulation of glucose uptake and inhibition of lipolysis, which occur very rapidly through insulin-responsive glucose transporter protein (GLUT 4) translocation or covalent modification of HSL. respectively. Insulin also stimulates fatty acid and triglyceride synthesis, through the induction of key lipogenic enzymes and induction of lipoprotein lipase. The data presented here are compatible with an increased energy turnover in the adipocytes derived from FOXC2 transgenic mice.
The white fat depots of FOXC2 transgenic mice had an ectopic expression of the brown fat specific marker UCP1 (Fig. 9). The origin of multilocular adipocytes in transgenic WAT (Fig. 7d) remains an enigma. It has been suggested that there is a pool of intraconveritble cells or small brown preadipocytes present in WAT. Studies on both rat and mice have demonstrated atypical occurrence of UCP1 in certain WAT depots previously thought to contain only white adipocytes (Cousin et al., 1992; Loncar, 1991). If submitted to cold or to treatment with a β₃-AR selective agonist, UCP1 expression was increased in WAT as in typical BAT and on histological sections one could identify small multilocular cells interspersed between the white adipocytes, which were shown to contain UCP1 by immunhistochemistry (Cousin et al., 1992; Ghorbani et al., 1997).
Furthermore, both UCP1 and β₃-AR mRNAs have been detected in white fat depots of human beings (Krief et al., 1913) and recently, it has been shown that cultures of human adipocytes derived from white fat depots express UCP1 after treatment with β₃-AR agonists (Champigny and Ricquier, 1996). Moreover, transgenic mice overexpressing β₁-AR in WAT and BAT have abundant appearance of brown fat cells in subcutaneous WAT (Soloveva et al., 1997). We would like to speculate that these suggested intraconveritble cells or small brown preadipocytes have undergone proliferation in our transgenic mice, readily detectable on histological sections as small multilocular cells (Fig. 8d), duc to the increased expression of β₃-AR. The FOXC2 transgene possibly actuates other proteins further down the signal transduction pathway finally leading to the induction of UCP1 expression. In addition, the levels of C/EBPα and PPARγ mRNAs in transgenic WAT reaches the ones in witd-type BAT (Fig. 10) and both of these transcription factors are known to induce UCP1 expression (Digby et al., 1998: Yubero et al., 1994). C/EBPα activates several adipocyte-specific genes and also genes involved in insulin action (Fig. 15), hence C/EBPα (-/-) cells show a complete absence of insulin-stimulited glucose transport, secondary to reduced gene expression and tyrosine phosphorylation for the insulin receptor and IRS-I (Wu et al., 19996). The WAT of FOXC2 transgenic mice have marked elevation of the mRNA levels for both C/EBPα and PPARγ, these transcription factors may in turn be responsible for upregulation of mRNA levels for aP2, LPL. UCP1, GLUT4, insulin receptor, and IRS-1 (Fig. 14)
It is interesting to note that the white adipocytes of FOXC2 transgenic mice have not just converted into brown adipocytes, in the meaning of mRNA expression, as they have for example higher levels of certain mRNAs (i.e. β₂-AR, insulin receptor, IRS-t, and IRS-2) than seen in any type of wild-type adipose tissue.
In the mice studied here, FOXC2 transgene expression was under the control of the aP2 promoter, which only functions in adipocytes and not in stem cells and probably neither in intraconveritble cells discussed above (Ailhaud et al., 1992). Considering the fact that aP2 is a late marker (Fig. 2) it is quite surprising that we obtain such a dramatic change in the characteristics of white adipocytes. Currently, it is not known if adipocyte dedifferentiation occurs in vivo, whereas it has been demonstrated in vitro that this process occurs and is induced by TNFα in human adipocytes (Petruschke and Hauner, 1993). Another interpretation for the occurrence of small multilocular cells in WAT of our transgenic mice could then be a dedifferentiation of originally white adipocytes followed by a conversion into the type of adipocytes observed in the FOXC2 transgenic mice.
The interscapular brown fat of FOXC2 transgenic mice weighed ~7.5 times as much as wild-type brown fat (Fig. 8a). This extreme hypertrophy might be explained by the increased expression of β₃- and β₂-AR mRNA seen in BAT of FOXC2 transgenic mice (Fig. 9). Chronic treatment with β₃-AR agonists increases body temperature and energy expenditure and it causes hypertrophy of the interscapular BAT, with several fold increases in the content of UCP1 and cytochrome oxidase (Himms-Hagen et al., 1994). The morphology of transgenic interscapular BAT is somewhat changed having larger fat droplets than wild-type BAT (Fig. 7a & b). This is not a feature of chronic β₃-AR agonist treatment, but there is a possibility that the upregulation of markers involved in insulin action (Fig. 9) and elevated levels of adipsin promotes the increased storage of triglycerides in brown adipocytes of transgenic mice. It has also been noticed before that elevated levels of UCP2 mRNA can be coupled to this phenotype (Enerback et al., 1997: Kozak el al., 1991).
Dysfunctional BAT seen in the ADDI/nSREBP-lc transgene (Shimomura et al., 1998) and genetically ablated BAT in the UCP1-DTA transgene (UCP1 promoter - diphtheria toxin A chain) (Lowell et al., 1993) leads to insulin resistance. Transgenic mice overexpressing ADD1/nSREBP-1c displays several features quiet opposite the ones of the FOXC2 transgene, including insulin resistance and NIDDM. FOXC2 transgenic mice displays a somewhat opposite change of expression pattern compared with that of ADD1/nSREBP-1c transgenic mice, there the mRNAs encoding PPARγ. C/EBPα, aP2, UCP I , adipsin, InsR, IRS-1, IRS-2, and GLUT4 all are downregulated. In our transgene all of this mRNAs are instead upregulated (Fig. 9). However, intriguingly our transgenic mice actually have raised levels of ADD1/SREBP1 mRNA in WAT (Fig. 9) somewhat mimicking the ADD1/nSREBP-1c transgene in that regard.
FOXC2 might be an important participant in the regulation of leptin expression, based on the fact that leptin mRNA levels are down-regulated in FOXC2 transgenic mice (most prominent in BAT; Fig. 9), and the ten-fold decrease of Ob promoter activity seen in cell culture experiments then cotransfected with FOXC2 expression plasmid (Fig. 4). In addition, leptin expression is inhibited by P3 -adrenergic stimuli (Mantzoros et al., 1996), which is presumed to be high in FOXC2 transgenic mice due to the up-regulation of β₃-AR mRNA levels.
The amount of food consumed by transgenic mice compared to that of wild-type did not differ (Fig. 8d), and no significant difference in body weight has been observed, predicting that the difference observed in total body lipid content must be compensated with an increased anabolism in FOXC2 transgenic mice. The FOXC2 transgenic mice most probably also are protected against developing diet-induced obesity, taking in consideration the observed insulin sensitivity (Fig. 13), the lower blood glucose levels and more efficient glucose elimination (Fig. 12) observed in our transgenic mice. Insulin sensitivity and/or resistance to diet-induced obesity have been observed for several other transgenic mouse models: targeted disruption of the RIIβ subunit of protein kinase A results in lean mice resistant to diet-induced obesity (Cummings et al., 1996), mice lacking the protein tyrosine phosphatase-1B gene (PTP- 1B) are insulin sensitive and resistant to obesity (Elchebly et al., 1999), aP2-UCP1 transgenic mice are prevented against genetic obesity (Kopecky et al., 1995), and transgenic mice overexpressing the β₁-AR in adipose tissue are resistant to obesity (Soloveva et al., 1997). Moreover, β₃-AR agonists have been found to have anti-diabetic effects in animal models of obesity and NIDDM; chronic dosing can improve glucose tolerance, increase insulin sensitivity and reduce fasting blood glucose levels (Cawthorne et al., 1992). FOXC2 is the only adipocyte specific gene that, directly or indirectly, regulates triglyceride metabolism, adrenergic regulation and insulin action in adipocytes. Actually, the FKHL14, is to our knowledge the only known gene that, in a concerted action, can counteract most, if not all, of the symptoms associated with obesity: hypertriglyceridemia, insulin resistance and most likely the associated clinical syndrome of NIDDM.
The apparent FOXC2 transgene dose responsive effect observed in WAT for the induction of UCP1, β₃-AR, and adipsin, may indicate a direct interaction for FOXC2 with the promoters of these genes. A schematic view of the hypothetical action of FOXC2 in adipocytes is shown in Fig. 14.
Proper activation of FOXC2 by drugs may decrease fat stores, while preserving skeletal muscle mass, by preventing fat assimilation during digestion and by increasing WAT lipolysis, BAT thermogenesis, and insulin action. Such drugs may thus prove useful in treating obesity and NIDDM as well as associated diseases. It is thus foreseen that an effective amount of a polypeptide encoded by the human FOXC2 gene, could be useful in methods for the treatment of medical conditions related to obesity.
Disclosed is a construct, or more specifically a gene construct or recombinant construct, comprising a human FOXC2 nucleotide sequence operably linked to an element selected from the group consisting of promoters, response elements, enhancer elements and mixtures thereof. The term "operably linked" as used herein means functionally fusing an element with a structural gene in the proper frame to express the structural gene under control of the element.
Preferably, the said element is a promoter, in particular an adipose-specific promoter such as the adipose-specific promoter of the murine gene encoding adipocyte P2 (Fig. 4), which can be isolated as described by Ross et al. (1990).
Preferably, the said FOXC2 nucleotide sequence is identical or substantially similar with SEQ ID NO: I of the Sequence Listing. However, the FOXC2 nucleotide sequence is not to be limited strictly to the sequence shown as SEQ ID NO: 1. It also encompasses nucleotide sequences carrying modifications like substitutions, small deletions, insertions or inversions, which nevertheless encode polypeptides having substantially the biochemical activity of the FOXC2 polypeptide.
Consequently, the said human FOXC2 nucleotide sequence is selected from:
(a) the nucleotide sequence shown as SEQ ID NO: 1;
(b) nucleotide sequences capable of hybridizing, under stringent hybridization conditions, to a nucleotide sequence complementary to the polypeptide coding region of a nucleotide sequence as defined in (a) and which codes for a biologically active FOXC2 polypeptide, or a functionally equivalent modified form thereof;
(c) nucleic acid sequence which are degenerate as a result of the genetic code to a nucleotide sequence as defined in (a) or (b) and which codes for a biologically active FOXC2 polypeptide, or a functionally equivalent modified form thereof; and
(d) nucleotide sequences which are at least 90% homologous, preferably at least 95% homologous, with the nucleotide sequence shown as SEQ ID NO: 1 in the Sequence Listing.
The term "stringent hybridization conditions" is known in the art from standard protocols (e.g. Ausubel et al) and could be understood as e.g. hybridization to filter-bound DNA in 0.5 M NaHPO₄, 7% sodium dodecyl sulfate (SDS), 1 mM EDTA at +65°C, and washing in 0.1xSSC / 0.1% SDS at +68°C.
Disclosed is a transgenic non-human mammalian animal whose genome comprises a gene construct as defined above, said animal being capable of expressing the human FOXC2 gene in its adipose tissue.
By "transgenic animal" is meant a non-human mammalian animal that includes a nucleic acid sequence which is inserted into a cell and becomes a part of the genome of the animal that develops from that cell. Such a transgene may be partly or entirely heterologous to the transgenic animal. Other transgenic mammals, including transgenic rodents (for example, hamsters, guinea pigs, rabbits, and rats), and transgenic pigs, cattle, sheep, and goats may be constructed by standard techniques.
One means available for producing a transgenic animal, with a mouse as an example, is as follows: Female mice are mated, and the resulting fertilized eggs are dissected out of their oviducts. The eggs are stored in an appropriate medium. DNA or cDNA encoding the FOXC2 gene is purified from a vector by methods well known in the art. Tissue specific regulatory elements, such as the adipocyte-specific aP2 promoter discussed above, may be fused with the coding region to permit tissue-specific expression of the trans-gene. The DNA, in an appropriately buffered solution, is put into a microinjection needle and the egg to be injected is put in a depression slide. The needle is inserted into the pronucleus of the egg, and the DNA solution is injected. The injected egg is then transferred into the oviduct of a pseudopregnant mouse, where it proceeds to the uterus, implants, and develops to term.
A transgenic mouse could preferably be derived from a genetically obese mouse. Genetically obese mice, such as ob/ob or db/db mice, are well known in the art.
Disclosed is an isolated cell line derived from the transgenic non-human mammalian animal, as well as a method for producing a transgenic non-human mammalian animal overexpressing the human FOXC2 gene, said method comprising chromosomally incorporating a gene construct comprising the human FOXC2 gene, together with suitable regulatory sequences, into the genome of said non-human mammalian animal.
Disclosed is also a method for studying the biological activity of a polypeptide encoded by the human FOXC2 gene, said method comprising the steps (i) producing a transgenic non-human mammalian animal overexpressing the human FOXC2 gene; and (ii) comparing the phenotype of the said transgenic non-human mammalian animal with a wild-type animal of the same species.
The invention provides biological screening assays for the identification of compounds that could be useful for the treatment of medical conditions related to obesity, or alternatively, to malnutrition. A "medical condition related to obesity" includes e.g. obesity, NIDDM, hypertension and hyperlipidemia. The said "medical condition related to malnutrition" includes e.g. anorexia, ineffective metabolism, and cancer.
Consequently, the invention provides a method for identifying a compound useful for the treatment of a medical condition related to obesity, said method comprising the steps (i) contacting a test compound with the human FOXC2 gene; and (ii) determining whether said test compound activates the expression of the human FOXC2 gene, such activation being indicative for a compound useful for the treatment of a medical condition related to obesity.
Disclosed is also a method of screening for a compound useful for the treatment of a medical condition related to obesity, said method comprising exposing a non-human mammalian animal to a test compound, and determining the activity of said human FOXC2 gene in said non-human mammalian animal, wherein an increase in said gene activity as compared to an untreated non-human mammalian animal being indicative of a compound useful for the treatment of a medical condition related to obesity.
The said non-human mammalian animal is preferably a mouse, for example an obese mouse. Mice can be rendered obese by administration of a high-fat diet. Alternatively, the mouse can be a genetically obese mouse, such as an ob/ob or db/db mouse.
In the methods described above, the activity of the human FOXC2 gene in said non-human mammalian animal, can advantageously be compared to the activity of the said human FOXC2 gene in a transgenic non-human mammalian animal expressing or overexpressing the said human FOXC2 gene.
In an alternative method for identifying a compound useful for the treatment of a medical condition related to obesity, the method comprises the steps (i) contacting a test compound with a polypeptide encoded by the human FOXC2 gene; and (ii) determining whether said test compound stimulates the biological activities of the said polypeptide, such stimulation being indicative for a compound useful for the treatment of a medical condition related to obesity. The term "biological activities", as used in this context, means e.g. enhancing the DNA-protein interaction between the FOXC2 polypeptide and target sequences in promoters of target genes. disclosed is a method for identifying a compound useful for the treatment of a medical condition related to malnutrition, said method comprising the steps (i) contacting a test compound with the human FOXC2 gene; and (ii) determining whether said test compound decreases or inhibits expression of the FOXC2 gene, such decrease or inhibition being indicative for a compound useful for the treatment of a medical condition related to malnutrition.
Disclosed is also a method of screening for a compound useful for the treatment of a medical condition related to malnutrition, said method comprising exposing a non-human mammalian animal, preferably a mouse, such as an obese mouse, to a test compound, and determining the activity of said human FOXC2 gene in said non-human mammalian animal, wherein a decrease in said gene activity as compared to an untreated non-human mammalian animal being indicative of a compound useful for the treatment of a medical condition related to malnutrition.
In an alternative method for identifying a compound useful for the treatment of a medical condition related to malnutrition, the method comprises the steps (i) contacting a test compound with a polypeptide encoded by the human FOXC2 gene; and (ii) determining whether said test compound decreases or inhibits the biological activities of the said polypeptide, such decrease or inhibition being indicative for a compound useful for the treatment of a medical condition related to malnutrition.
In the above discussed methods for identifying compounds decreasing or stimulating FOXC2 biological activity, other genes encoding forkhead proteins can conveniently be used for comparison (counter-screening) in order to determine the specificity of the test compound. Such forkhead genes, e.g. freac-3 and freac-4, are disclosed e.g. by Pierrou et al. (1994) EMBO Journal 13, 5002-5012.
The skilled person will appreciate that other polypeptides, interacting in the same biological pathways as the FOXC2 polypeptide, will be useful in screening methods for the identification of agents, which agents are useful for the treatment of medical conditions related to obesity or malnutrition. Such alternative target polypeptides could be identified e.g. by a yeast two-hybrid assay (cf. Example 11), or by microarray technology (cf. Example 14). Consequently, disclosed is a method for identifying an agent useful for the treatment of a medical condition related to obesity, said method comprising the steps:
(i) identifying a target polypeptide interacting with the FOXC2 polypeptide;
(ii) contacting a candidate agent with the said target polypeptide; and
(iii) determining whether said candidate agent stimulates the biological activities of the FOXC2 polypeptide, such stimulation being indicative for a compound useful for the treatment of a medical condition related to obesity.
The phrase "determining whether said candidate agent stimulates the biological activities of the FOXC2 polypeptide" is intended to comprise, for instance, determining whether the candidate agent is capable of increasing expression of the FOXC2 polypeptide, or whether the candidate agent is capable of otherwise modulating the biological activities of the FOXC2 polypeptide. The said biological activities of the FOXC2 polypeptide are discussed in detail in the Examples below, and comprises e.g. a reduction of total lipid content in test animals.
For therapeutic uses, the compositions or agents identified using the methods disclosed herein may be administered systemically, for example, formulated in a pharmaceutically acceptable buffer such as physiological saline. Preferable routes of administration include, for example, oral, subcutaneous, intravenous, intraperitoneally, intramuscular, or intradermal injections, which provide continuous, sustained levels of the drug in the patient. Treatment of human patients or other animals will be carried out using a therapeutically effective amount of an identified compound in a physiologically acceptable carrier. Suitable carriers and their formulation are described, for example, in Remington's Pharmaceutical Sciences by E. W. Martin. The amount of the active compound to be administered varies depending upon the manner of administration, the age and body weight of the patient, and with the type of disease and extensiveness of the disease. Generally, amounts will be in the range of those used for other agents used in the treatment of obesity and diabetes.
The human FOXC2 gene could be used in gene therapy of medical conditions related to obesity. Disclosed is thus a method of treating obesity in a human, comprising (i) administering to the said human a vector comprising a human FOXC2 DNA sequence operably linked to a promoter; and
(ii) allowing the said human to express a therapeutically effective amount of a polypeptide encoded by said human FOXC2 gene. A gene delivery system including said vector, comprising a human FOXC2 DNA sequence operably linked to a promoter, is also disclosed.
The FOXC2 gene should be operably linked to at least one element which allows for expression of the gene when introduced into the host cell environment. These sequences include promoters, response elements, and enhancer elements. Preferred is the adipose-specific promoter/enhancer of the murine gene encoding adipocyte P2
The heterologous gene may be delivered to the organism using a vector or other delivery vehicle. DNA delivery vehicles can include viral vectors such as adenoviruses, adeno-associated viruses, and retroviral vectors. See, for example: Chu et al. (1994) Gene Ther 1: 292-299; Couture et al. (1994) Hum Gene Ther 5:667-677; and Eiverhand et al. (1995) Gene Ther 2: 336-343. Non-viral vectors which are also suitable include DNA-lipid complexes, for example liposome-mediated or ligand/poly-L-Lysine conjugates, such as asialoglyco-protein-mediated delivery systems. See, for example: Feigner et al. (1994) J. Biol. Chem, 269: 2550-2561; Derossi et al. (1995) Restor. Neurol. Neuros. 8: 7-10; and Abcallah et al. (1995) Biol. Cell 85: 1-7.
If a vector is chosen as the delivery vehicle for the gene, it may be any vector which allows expression of the gene in the host cells. It is preferable if the vector also is one that is capable of integrating into the host genome, so that the gene can be expressed permanently. Ad (adenovirus) vectors have been exploited for the delivery of foreign genes to cells for a number of reasons, including the fact that Ad vectors have been shown to be highly effective for the transfer of genes into a wide variety of tissues in vivo and the fact that Ad infects both dividing and non-dividing cells. The vector is administered to the host, generally by intravenous injection. Suitable titers will depend on a number of factors, such as the particular vector chosen, the host, strength of promoter used and the severity of the disease being treated.
Alternatively, it is contemplated that in some human disease states, preventing the expression of, or decreasing the activity of, the human FOXC2 gene will be useful in treating disease states. It is contemplated that antisense therapy or gene therapy could be applied to negatively regulate the expression of the human FOXC2 gene. Antisense nucleic acids (preferably 10 to 20 base-pair oligonucleotides) capable of specifically binding to FOXC2 expression control sequences or FOXC2 RNA are introduced into cells (e.g. by a viral vector or colloidal dispersion system such as a liposome). The antisense nucleic acid binds to the FOXC2 target nucleotide sequence in the cell and prevents transcription and/or translation of the target sequence. Phospborothioate and methylphosphonate antisense oligonucleotides are specifically contemplated. The antisense oligonucleotides may be further modified by poly-L-lysine, transferrin polylysine, or cholesterol moieties at their 5'-end. Suppression of FOXC2 expression at either the transcriptional or translational level is useful to generate cellular or animal models for diseases/conditions characterized by aberrant FOXC2 expression.
Throughout this description the terms "standard protocols" and "standard procedures", when used in the context of molecular biology techniques, are to be understood as protocols and procedures found in an ordinary laboratory manual such as: Current Protocols in Molecular Biology, editors F. Ausubel et al., John Wiley and Sons, Inc. 1994, or Sambrook, J., Fritsch, E.F. and Maniatis, T., Molecular Cloning: A laboratory manual, 2nd Ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY 1989.

EXPERIMENTAL METHODS

Cloning and DNA construct

A human adipose tissue λgt11 cDNA library (Clontech) was screened with a probe mixture corresponding to the conserved fork-head domain derived from: FOXC1, FOXD1, FOXL1, and FOXA1. Hybridization was carried out at low stringency, i.e. 6xSSC at +60°C, post-hybridization washes at 0.5xSSC at +60°C. One of the positive recombinants harboring a 2.1 kb insert was subcloned and sequenced. A 5.4-kb EcoRV-SmaI fragment was excised from pBluescript II SK(+) vector containing the 5.4-kb promoter/enhancer of the mouse aP2 gene and ligated into the EcoRV-SpeI blunt site of pBluescript II SK(+) vector containing the 2.1 kb FOXC2 cDNA. A 7.6 kb XhoI blunt fragment containing the aP2 promoter/enhancer followed by the FOXC2 cDNA was excised from the above plasmid and ligated into the EcuRV site of the pCB6+ vector, which .contains a polyadenylation signal from the human growth hormone gene. After these procedures the resulting 8.2-kb fragment, harboring the aP2-FOXC2 construct with polyadenylation signal, was flanked by the unique sites NotI and AgeI. The plasmid was sequenced over ligation sites.

Transgenic mice

Construct DNA (aP2-FOXC2), purified using Qiagen kit, according to manufacturer's instructions, was injected into the male pronucleus of (C57BL6 x CBA) F, zygotes, cultured over night and transferred to pseudopregnant females. Tg founder lines were back-crossed to C57BL6/J for four generations. Mice were feed a standard chow with 4% fat content. In experiments with high fat diet mice were fed either a chow with 58% fat or a control diet with 11.4% fat (on a caloric basis; Research Diets) for 7 weeks. High fat chow has a total energy content of 23.4KJ/g, control diet 12.6KJ/g.

Histology

Tissues were fixed over night in 4% paraformaldehyde in PBS at +4°C, dehydrated, embedded in paraffin, sectioned (6-8 µm) and stained with haematoxylin and eosin.

Serum and lipid analysis

Plasma insulin was determined radioimmunochemically with the use of a guinea pig anti-rat insulin antibody, ¹²⁵I-labeled porcine insulin as tracer and rat insulin as standard (Linco). Free and bound radioactivity was separated by use of an anti-IgG (goat anti-guinea pig) antibody (Linco). The sensitivity of the assay is 17 pmol/l and the coefficiency of variation is less than 3% at both low and high levels. Plasma glucose was determined with the glucose oxidase method and FFA was measured photometrically. Plasma glucagon was determined radioimmunochemically with the use of a guinea pig antiglucagon antibody specific for pancreatic glucagon, ¹²⁵I-labelled-glucagon as tracer, and glucagon standard (Linco). Free and bound radioactivity was separated by use of an anti-IgG (goat anti-guinea pig) antibody (Linco). The sensitivity of the assay is 7.5 pg/ml and the coefficient of variation is less than 9%. Blood levels of serum cholesterol and triglycerides were determined by fully enzymatic techniques 39,40. Total body lipid was assessed using alcoholic hydroxide digestion with saponification of all lipids, neutralization, followed by enzymatic determination of glycerol.

Intravenous glucose tolerance test

The mice were anesthetized with an intraperitoneal injection of midazolam 0.4 mg/mouse (Hoffman-La-Roche) and a combination of fluanison (0.9 mg/mouse) and fentanyl 0.02 mg/mouse (Janssen). Thereafter, a blood sample was taken from the retrobulbar, intraorbital, capillary plexus in heparinized tubes, and D-glucose 1g/kg (British Drug Houses) was injected rapidly intravenously. New blood samples were taken after 1. 5, 20, and 50 minutes. Following immediate centrifugation at +4°C, plasma was separated and stored at -20°C or until analysis.

Northern blot

cDNA probes for mouse FoxC2, aP2, ADD-1/SREBP1, coxII, adipsin, β_1-3-AR, GLUT4, IR, IRS1, and IRS2 were prepared by RT-PCR by use of first-strand cDNA from mouse epididymal fat poly(A)⁺ RNA. The PCR primers used to generate these probes were as follows:
cDNA probes were radiolabeled with [α-³²P]dCTP (3000 Ci/mmole) by the random labeling method. Total RNA from mice in each group was pooled, and aliquots of 12 µg were separated on an agarose gel. The filters were hybridized with ³²P-labeled probe (10⁶ cpm/ml) for 1h at 62°C with QuikHyb solution (Stratagene) and washed with 0.1% SDS/0.1 x SSC at +62°C for 3x20 min.

Transfections and reporter gene analysis

Non-confluent cultures of 3T3-L1 adipocytes were transfected with a CAT reporter (pCAT) driven by the human RIα proximal promoters upstream of the alternatively spliced 1a and 1b leader exons (nucleotides 1509 to 2470 GenBank # Y07641). To control transfection efficiency a pGL3control (Promega) luciferase-encoding vector was used. In cmransfections a FOXC2 expression vector or vector void of insert was used. Transtcctions were carried out using lipofectamine (Gibco), followed by CAT and luciferase assays.

PKA immunoblotting and kinase activity

WAT and BAT were treated by a Polytron tissue homogenizer (3 x 15 s) and sonicated, on ice, in a buffer containing 10 mM potassium phosphate, pH 6.8, 150 mM sodium chloride, I mM EDTA, 10 mM CHAPS and protease inhibitors, and centrifuged (15.000 x g) to remove insoluble material. Protein concentrations were determined by Bradford assays (BioRad). For immunoblotting, 30 µg of protein was separated by 10% SDS-PAGE. transferred to PVDF membranes and incubated with anti-RIα and anti-RIIβ mAb. Primary antibodies were detected by HRP-conjugated anti-mouse IgG (Transduction Laboratoriea. 1:5000) and ECL (Amersham). PKA activity was measured using Kemptide (Leu-Arg-Arg-Ala-Ser-Leu-Gly) as substrate in the absence or presence of varying concentrations of cAMP. The low levels of activity not inhibited by PKI (2 µM) were subtracted to determine PKA-specific activity.

EXAMPLES OF THE INVENTION

Additional features of the invention will be apparent from the following Examples. Examples 1 to 10 are actual, while the remaining Examples are prophetic.

EXAMPLE 1: Isolation of FOXC2 from human abdominal fat tissue

To identify presumptive winged helix genes that are expressed in adipose tissue we screened a Human Fat Cell 5'-STRETCH plus cDNA Library (Clontech) using a low stringency hybridization strategy with a mix of cDNA probes corresponding to DNA-binding domains from different winged helix proteins, to cover the variation between different family members. By this technique, we were able to identify three different forkhead genes, termed FKHL5, FKHL14, and FKHL18, FKHL5 was known to be expressed exclusively in lung and placenta (Pierrou et al., 1994) and expression in adipose tissue could not be detected as judged by Northern blot analysis (data not shown). FKHL18 was identified as a novel member of the forkhead family (Cederberg et al., 1997) having a very high homology with the forkhead motif of the mouse gene fkh-3 (Kaestner et al., 1993). Sequence from outside the forkhead motif have not yet been published for fkh-3 but with regard to the discrepancy of the expression patterns, with FKHL18 being expressed in arterial vessel wall (aorta) and to a lower extent in kidney and fkh-3 being expressed in a wide variety of tissues, they are presumed to constitute two different genes. We were not able to detect any expression of FKHL18 in adipose tissue (data not shown). The third identified gene, FKHL14 (hereinafter referred to as FOXC2: Miura, N. et al. (1997) Genomics 41, 489-492), was shown to be expressed exclusively in human adult adipose tissue by Northern blot analysis (Fig. 3a). The mouse homologue of FOXC2 is known as Mfh1 and is expressed in dynamic patterns in the paraxial mesoderm of the trunk and head, in the mesenchyme and endothelial cells of the branchial arches, and in many other sites in the embryo (Kaestner et al., 1996; Miura el al., 1993: Winnier et al., 1997). It has been demonstrated by gene targeting experiments that Mfh1 plays a crucial role during embryonic development. Homozygous null mutants died pre- and perinatally with multiple skeletal and cardiovascular defects, including defects in the neurocranium and vertebral column, interruptions or coarctations of the aortic arch, and ventricular septal defects (Iida et al., 1997; Winnier et al., 1997). Heterozygous mice were indistinguishable from wild-type and appeared healthy. The expression of Mfh1 in adult tissues was restricted to WAT and BAT (Fig. 3b).

EXAMPLE 2: Physiological studies of FOXC2

In a Northern blot experiment we used RNA from collagenase prepared adipocytes and cells with lower triglyceride content, mostly preadipocytes/adipocytes and cells of stroma/vascular origin, in order to identify the cell type expressing FoxC2 (Fig. 3c). As can be deduced from Fig. 3c, FoxC2 expression is highest in the adipocyte fraction with a lower level of expression in stroma/vascular cells, most likely due to the presence of adipocytes with lower triglyceride content - since the adipocyte specific marker LPL (lipoprotein lipase) also is expressed by these cells.
To address the general question of the physiological role/regulation of FoxC2 we preformed the following experiment: 3T3-L1 adipocytes were stimulated separately and in combination with the cAMP-inducing agent forskolin, the protein kinase C-activator TPA and Ca²⁺-ionophore A23187 to mimic signals elicited down-stream of G-protein coupled receptors. Whereas forskolin alone or in combination with Ca²⁺-ionophore produce a 3-fold increase in steady state levels of FoxC2 mRNA (Fig. 3d), Ca²⁺-ionophore by itself does not appear to regulate FoxC2 levels. In contrast, TPA and combinations that include TPA give a strong increase (9 to 10-fold) in FoxC2 mRNA (Fig. 3d). This suggests that FowC2 is regulated by intracellular events similar to those elicited by G-coupled hormone receptors.

EXAMPLE 3: Generation of transgenic mice overexpressing FKHL14

To elucidate whatever function FOXC2 might have in vivo we decided to create transgenic mice overexpressing FOXC2 in adipose tissue. To achieve overexpression of FOXC2 in both white and brown adipose tissue, we prepared a transgene construct (Fig. 4a) encoding FOXC2 driven by a 5.4-kb DNA fragment containing the adipose-specific enhancer/promoter of the gene encoding adipocyte P2 (Ross et al., 1990). Integration positive mice were identified using Southern blot analysis (Fig. 4b).
We studied three lines of transgenic mice (A, B, and C) that were derived from independent founders. Transgene expression, analyzed by Northern blot using a FOXC2 (human specific) probe, was detected at high levels in both WAT and BAT for all three founders. The three different founders had a slight difference in expression levels of the transgene in white fat, founder A having the highest and founder B the lowest, while the expression levels in brown fat were equal (Fig. 5c). All of the transgenic mice used for the study were hemizygous for the transgene and from the second to fourth generation. The transgenic mice appeared normal at external inspection and the transgenic allele was propagated with the expected mendelian distribution. Fed a standard rodent chow diet (4% fat, 18.5% protein, and 55.7% sucrose) weight gain was studied for all founders from 4 weeks up to 6 months of age with no significant difference between nontransgenic and transgenic littermates noticed (data not shown).
We selected three independent founder lines, named tg-A, tg-B and tg-C with tg-A having the highest, tg-B the lowest and tg-C an intermediate level of FOXC2 expression in WAT. There is a clear dose-response relation between the expression level of the transgene and reduction in the relative weight of the intra-abdominal WAT depot (Fig. 5a). A similar dose-response pattern exists when the weight ratios of intra-abdominal WAT to interscapular BAT are compared (Fig. 5b). The relative weight of the interscapular BAT depot is increased in tg animals but does not exhibit any dose-response association (Fig. 5a), which is in accordance with the fact that there is no difference between tg-A, tg-B and tg-C in expression of the transgene in BAT.

EXAMPLE 4: WAT of FOXC2 transgenic mice morphologically resembles BAT

The interscapular brown adipose tissue depot and the intrabdominal white adipose tissue were examined in 5-months-old mice (Fig. 6). Interscapulary, transgenic mice had a greatly enlarged bilobed (dissected apart in the picture) fat pad with the "looks" of brown adipose tissue without the usual coverage of white adipose tissue (Fig. 6b), which normally have to be dissected to uncover the interscapular BAT depot (Fig. 6a). An exposed abdominal view of FOXC2 transgenic mice revealed an obvious decrease of intrabdominal fat mass and also a distinct change in the appearance towards the brown adipose tissue phenotype (Fig. 6d), when compared to the large, pale lipid-storing intrabdominal fat pad of wild-type mice (Fig. 6c). The adipose tissue change in appearance and mass between transgenic and non-transgenic mice was very striking then the depots had been dissected out (Fig. 6e & f).
Histological analysis of BAT and WAT from 5-months-old mice revealed profound differences between transgenic and non-transgenic tissues. The majority of adipocytes in brown fat of the transgenic mice contained few markedly enlarged fat droplets (Fig. 7b), instead of small multilocular fat droplets typical for BAT (Fig. 7a). Adipocytes in intrabdominal white fat of the transgenic mouse showed heterogeneity of size, all of them having a clearly reduced size (Fig. 7d). This was in contrast to WAT from wild-type mouse, which consisted of large adipocytes of uniform size filled with a large, unilocular lipid-storing vacuole (Fig. 7c).
In a cold adaptation experiment (4°C. 4 hours) tg mice display a clear reduction in size and number of triglyceride droplets in BAT (Fig. 7 e-h). This indicates that the changes in gene expression induced by the transgene will allow a net accumulation of triglyceride at room temperature (22°C) whereas these triglycerides are metabolised at 4°C. In a recent report it has been suggested that, apart from WAT and BAT, aP2 is also expressed in activated macrophages. Measurements of two cytokines IL-12 and IL-18, both implicated in macrophase activation, showed no difference between tg and wt mice (data not shown).
To further examine the change of size of fat depots in transgenic mice, we compared the weights of intrabdominal WAT depots and interscapular BAT depots of 5-months-old wild-type females (n=3) and FOXC2 transgenic littermates (n=3). In transgenic mice there was a decrease in weight of the intrabdominal WAT depot (-40%) whereas the interscapular BAT depot showed a marked increase (-7.5 times; Fig. 8a). In consequence the ratio between weights of the intrabdominal fat depot and the interscapular brown fat depot was greatly decreased (Fig. 8b). No significant difference in body weight could be detected between transgenic and non-transgenic mice (Fig. 8c), nor could any difference in food consumption be observed then measured during a time period of two months (Fig. 8d).

EXAMPLE 5: Altered gene expression in FOXC2 transgenic mice

Figure 9 shows an analysis of mRNA steady state levels in white and brown adipose tissue of wild-type mice and the three independent transgenic founders. In wild-type mice, the mRNA for uncoupling protein 1 (UCP1) was detectable only in BAT, but in the transgenic mice expression could be detected in WAT, in a dose responsive manner in proportion to the expression level of transgenic FKHL14. The WAT blot and BAT blot had different exposure times, 2 days and 30 minutes respectively. UCP2 seemed to have a tendency to be regulated in the opposite direction as compared with UCP in WAT of transgenic mice. The uncoupling protein expressed in skeletal muscle and BAT, UCP3. showed greatly decreased levels in transgenic BAT. The cytochrome c-oxidase subunit 11 (Coxll), a gene encoded by the mitochondrial genome, was used as a marker for density of mitochondria. The density of mitochondria in WAT and BAT from transgenic animals appeared to be elevated and to a lesser extent reduced, respectively. In wild-type mice, the mRNAs of β₁- and β₃-AR were much lower in WAT than in BAT. The FOXC2 transgene abolished this discrepancy, raising these mRNAs selectively in WAT so that they became equal, or in the case of β₃-AR even higher, compared to the levels in BAT. The β₂-AR mRNA level was elevated in both WAT and BAT of transgenic mice, reaching levels not seen in nor WAT or BAT of wild-type littermates. White fat depots of transgenic animals exhibited profound increment in four of its mRNAs that are associated with fully differentiated adipocytes, that is. PPARγ2, C/EBPα, aP2, and adipsin. Furthermore PGC-I, a co-activator of PPARγ2, was upregulated in both WAT and BAT. The mRNA for ADDt/SREBP was elevated in WAT for all three founders. The transgenic animals demonstrated a reduction of the amount of leptin mRNA with the most distinct effect in BAT. Steady state levels of LPL mRNA appear to have increased slightly in WAT of transgenic mice. All investigated markers involved in insulin action were upregulated: the insulin receptor (InsR). IRS-I, IRS-2, and insulin-responsive glucose transporter-4 (GLUT4). The upregulation was most evident in WAT. GAPDH was used as a control to verify equal amounts of total RNA in the different lanes.

EXAMPLE 6: Triglyceride content is altered in FOXC2 transgenic mice

Serum triglyceride content wa:; analyzed for 14-weeks-old wild-type males (n=4) and FOXC2 transgenic littermates (n=4) fed ad libitum. The transgenic animals exhibited a ~60% reduction in serum triglyceride levels (Fig. 10).
Total body lipid content was assessed using alcoholic potassium hydroxide digestion with saponification of all fats, neutralization, and then enzymatic determination of glycerol (Triglyceride kit, Sigma) as described previously (Salmon and Flatt, 1985). The assay was carried out for 6-months-old wild-type males (n=4) and FOXC2 transgenic littermates (n=4) fed ad libitum. The total body lipid content was reduced to 10% of the body weight for transgenic mice compared with the normal 30% of body lipid noted for wild-type mice (Fig. 11).

EXAMPLE 7: Lower blood glucose and more efficient glucose elimination in FOXC2 transgenic mice

Nonfasting blood glucose levels were measured for 10-weeks-old wild-type males and females (n=5+5), and FOXC2 transgenic littermates (n=5+5) fed ad libitum. The transgenic animals showed a significant 16% reduction in nonfasting blood glucose levels (Fig. 12a).
A glucose tolerance test was performed on 10-weeks-old wild-type males and females (n=5+5) and FOXC2 transgenic littermates (n=5+5) fed ad libitum. Plasma glucose levels peaked at one minute after intravenous glucose administration, and thereafter plasma glucose levels returned to baseline levels within the 50-minutes study period. Transgenic mice displayed an enhanced glucose elimination, with plasma glucose levels significantly lower than wild-type littermates at 0, 20, and 50 minutes (P<0.05; P<0.001; P<0.05) (Fig. 12b). Data are means of both males and females as no difference between gender was noticed.

EXAMPLE 8: Increased insulin sensitivity in FOXC2 transgenic mice

Non-fasting plasma insulin levels in FOXC2 transgenic mice were analyzed using the same group of animals as was used for blood glucose measurements. The concentration of plasma insulin in FOXC2 transgenic mice before the start of the glucose tolerance test were reduced to -50% of the levels registered for wild-type littermates (Fig. 13a). The rapid intravenous injection of glucose (1 g/kg) raised plasma insulin levels 4-fold in wild-type mice and 10-fold in FOXC2 transgenic littermates after one minute (Fig. 13c). Thereafter, plasma insulin levels rapidly returned toward baseline values observed before the glucose load, with transgenic mice having significantly lower levels at 20 and 50 minutes (P<0.05; P<0.05) (Fig. 13b). Data are means of both males and females as no difference between gender was noticed.
In mice on a high fat diet, there are significantly lower weight gains in transgenic mice as compared with wt. In females the weight gain is 39% (p<0.02; Fig. 15a) lower as compared with wt females and for males the difference is 21% (p<0.03; Fig. 15b). These findings highlight FOXC2, not only as a gene of importance for adipose tissue distribution, morphology and gene cxprcssion profile, but also, more importantly, as a major regulator of general lipid and glucose metabolism including protection against diet induced weight gains.

EXAMPLE 9: FOXC2 regulates body composition, serum lipids and insulin sensitivity

Several physiological tests and measurements of critical metabolites with relevance for obesity, insulin resistance and type 2 diabetes were carried out in order to assess the impact of increased FOXC2 expression on systemic lipid and glucose metabolism. We assayed total body lipid content on whole carcasses using the alcoholic potassium hydroxide digestion method and found a decrease from 30% total lipids in carcasses from wt mice as compared with only 10% in tg mice (p<0.0004; Fig. 16a). There is also a highly significant reduction in serum triglyceride levels by 57% (p<0.004; Fig. 16b), whereas there is no significant change in serum cttolesterol levels (Fig. 16c). FFA are lowered from 0.92mcq/l to 0,63meq/1 in tg animals (p<0.02; Fig. 16d). In ad libitum fed animals we note a decrease in plasma glucose levels by 10% (p<0.01; Fig. 16e) and plasma insulin levels are down by 43% (p<0.001; Fig. 16f). In mice on a high fat diet, the weight gain is 28% lower (p<0.01; Fig. 16g) for tg mice as compared with wt litter mates. Although lipid content in tg and wt mice are increased after a high fat diet tg mice still resist lipid accumulation to the same degree as is the case for wt litter mates, a 49% decrease in tg mice as compared with wt (p<0.0001; Fig. 16h). On a control diet (4.8% fat) tg and wt mice display no signs of differences in metabolic efficiency as judged by calculating the ratio between weight gain and weight of food eaten (Fig. 16i). When fed a high fat diet (35.9% fat) tg mice appear less efficient in their metabolism since they need to eat more for each gram of increase in body weight (a reduction by 30% p<0.01; Fig. 16i). These findings are interesting since they suggest that metabolic efficiency, in FOXC2 tg can be regulated in response to food composition. There are no significant differences in serum glucagon levels, body weight or food consumption (on standard diet) between wt and tg animals (not shown) nor have we observed any significant gender differences.
In an intravenous glucose tolerance test, plasma glucose was assayed at 0, 1, 5, 20, 50 and 75 minutes after glucose administration as depicted in Fig. 17a. Plasma glucose levels for tg mice on control diet are significantly lower at 0, 20 and 75 minutes (p<0.05), and at 50 minutes (p<0.02). The insulin curve for the same experiment exhibit lower insulin levels for tg mice (Fig. 17b) at 0 minutes (p<0.02), at 1, 5 and 20 minutes (p<0.05) and at 50 and 75 minutes (p<0.001). When on a high fat diet the difference after an intravenous glucose tolerance test is much more pronounced (Fig. 17c and d). Glucose levels are lower in tg mice as compared with wt at 0, 5, 20, 50 and 75 minutes (p<0,001; Fig. 17c). Insulin levels are dramatically lowered in tg mice at all time points (p<0.001; Fig. 17d). It is quite extraordinary that tg mice on a high fat diet retain a plasma insulin profile almost identical to that observed when on a standard diet while wt mice display almost a 3-fold increase in insulin plasma levels (Fig. 17 b, d). In spite of this wt mice exhibit a clear increase in glucose levels while tg mice show a much more modest increase in glucose values (Fig. 17 a, b). These findings highlight FOXC2, not only as a gene of importance for adipose tissue distribution, morphology and gene expression profile, but also, more importantly, as a major regulator of general lipid and glucose metabolism including protection against diet induced insulin resistance. EXAMPLE 10: Increased sensitivity of the β-adrenergic/cAMP/protein kinase A pathway
The induction of the cAMP-regulated ucpl in WAT, the hypertrophy of BAT, the decrease of intra-abdominal WAT depots and the up-regulation of mRNAs encoding β-ARs suggest that an increased perturbation and sensitivity in the β-adrenergic/cAMP/protein kinase A (PKA) signaling pathway may contribute to the phenotype of mice over-expressing FOXC2. In cotransfection experiments, using 3T3-L1 adipocytes, we show that FOXC2 increases reporter gene activity of a construct driven by the promoter of the RIα gene (encodes the regulatory subunit Iα of PKA; Fig. 18a), whereas no such regulation could be observed for the RIIβ promoter (data not shown). Consistent with these findings we also demonstrate increased RIα mRNA levels in adipose tissue from tg mice as compared with wt litter mates (Fig. 18a, insert), in a dose dependent manner with regard to transgene expression. This is accompanied by elevated levels of RIα protein and unchanged (WAT) or decreased (BAT) levels of RIIβ protein in tg mice (Fig. 18b). However, basal and total PKA activity is decreased in tg WAT and BAT (Fig. 18c). This may be due to an increased sensitivity to activation by cAMP, dissociation and thereby degradation of PKA holoenzyme. The PKA type I holoenzyme (RIα₂C₂) binds cAMP with higher affinity and activates more easily than the PKA type 2 enzyme (RIIβ₂C₂), normally expressed in WAT and BAT. Indeed, PKA from WAT of FOXC2 tg mice with elevated protein levels of RIα (Fig. 18d, insert), activates more easily than PKA from WAT of non-tg litter mates (Fig. 19d, K_act of 140 and 250 nM, respectively) although protein levels of RIIβ appear unchanged (Fig. 18d, insert). Thus, adipocytes from FOXC2 tg mice will have a lower threshold for PKA activation by adrenergic stimuli as compared with wild type litter mates due to a PKA isozyme switch. This is in accordance with what has been reported for mice with targeted disruption of the RIIβ gene, where an isozyme-switch from PKA type II (RIIβ₂C₂) to PKA type I (RIα₂C₂) with a change in K_act from 220 nM to 80 nM in WAT leads to a lean mouse with similar phenotype as the FOXC2 tg mouse. In addition to the increased sensitivity of the PKA-system in FOXC2 tg adipose tissue, examination of the β-adrenergic sensitivity of WAT-adipocytes from FOXC2 tg and wt litter mates revealed distinct differences. Whereas stimulation of wt adipocytes with a non-selective β-agonist leads to a 4 to 5-fold increase in cAMP levels at 1 min and a rapid desensitization of the signal, stimulation of of tg adipocytes leads to a strong (10-fold), prolonged and sustained increase in cAMP levels which is not desensitized at 10 min (Fig. 18e). Furthermore, β₃-agonist stimulation of adipocytes prepared from tg WAT displays a distinct increase (4-fold) in cAMP levels with elevated levels over 10 min (Fig. 19f). In contrast, little or no β₃-agonist response is observed in adipocytes from wt WAT. These observations are in agreement with the strong up-regulation of β_1-2-AR and the introduction of β₃-AR (which is virtually absent in wt) in tg WAT and indicate that the sensitivity of β-adrenergic/cAMP/PKA pathway in WAT from FOXC2 tg mice is increased at several levels.

EXAMPLE 11: Interaction trap / two-hybrid system

In order to assay for polypeptides interacting with the FOXC2 polypeptide, the interaction trap/yeast two-hybrid (Y2H) library screening method is used. This in vivo assay in was first described in Fields & Song (1989) Nature 340, 245-246. A recent method named Sos recuitment system (SRS) has been described by Aroheim & Karin (1997) Mol. Cell. Biol. 17, 3094-3102. The SOS system differs from the original yeast 2-hybrid for at the interaction between bait and prey takes place in the cytoplasm. A kit for the SOS-Y2H is available from Stratagene, La Jolla-CA, USA (Cyto TrapTwo-Hybrid System).
A fusion of an FOXC2 nucleotide sequence and the human Sos catalytic domain without its C-terminal regulatory domain (Bait) is constructed in an appropriate plasmid (e.g. pSos) using standard subcloning techniques. Similarly, a myristylation sequence fusion library (Prey) is constructed in a second plasmid (e.g. pMyr) from cDNA of potential binding proteins. The Sos fusion construct is verified by sequencing, and tested for its inability to allow growth of cdc25H yeast strain at the restrictive temperature of 37°C and cell toxicity, both of which would prevent a successful two-hybrid analysis. The Myr sequence anchors the Myr/library fusion polypeptides to the plasma membrane and its expression depends on the sugar-containing medium used. Yeast cells are transformed (ca. 5-10 x 10⁶ transformants/mg DNA) with both the Sos and Myr library fusion plasmids according to standard procedures. In vivo binding of Sos/(FOXC2) with Myr/library proteins results in a recruitment of the hSos protein to the membrane, thereby activating the Ras-signaling pathway and allowing the cdc25H yeast cells to grow at 37°C. Yeast cells are first plated on a glucose media lacking the amino acids Leu and Ura to select both plasmids. After 4-5 days at 25°C, plates are used for replica plating onto galactose (-Leu, -Ura) plates incubated at 37°C for 3-10 days . Colonies that are growing are first tested for their ability to grow at 37°C depending of the sugar present in the medium. Those clones that show growth in galactose compared to glucose are considered candidates. To test the specificity of the of the library plasmids, plasmid DNA is extracted from candidate clones and used to cotransform cdc25H cells with either the specific bait or a non-relevant bait. Insert DNA is sequenced to verify the presence of an open reading frame fused to the Myr sequence and to determine the identity of the interacting protein.

EXAMPLE 12: Mobility shift DNA-binding assay

A gel electrophoresis mobility shift assay, according to standard procedures, can rapidly detect specific protein-DNA interactions. Probe DNA (<300 bp) is obtained from synthetic oligonucleotides, restriction endonuclease fragments, or PCR fragments and end-labeled with ³²P. An aliquot of purified FOXC2 (ca. 15 µg) or crude FOXC2 extract (ca. 15 ng) is incubated at constant temperature (in the range 22-37°C) for at least 30 minutes in 10-15 µl of buffer (i.e. TAE or TBE, pH 8.0-8.5) containing radiolabeled probe DNA, nonspecific carrier DNA (ca. 1 µg), BSA (300 µg/ml), and 10% (v/v) glycerol. The reaction mixture is then loaded onto a polyacrylamide gel and run at 30-35 mA until good separation of free probe DNA from protein-DNA complexes occurs. The gel is then dried and bands corresponding to free DNA and protein-DNA complexes are detected by autoradiography.

EXAMPLE 13: Reporter gene assay to identify modulating compounds

Reporter gene assays are well known as tools to signal transcriptional activity in cells. (For a review of chemiluminescent and bioluminescent reporter gene assays, see Bronstein et al. (1994) Analytical Biochemistry 219, 169-181.) For instance, the photoprotein luciferase provides a useful tool for assaying for modulators of FOXC2 activity. Cells (e.g., CHO cells or COS 7 cells) are transiently co-transfected with both a FOXC2 expression construct and a reporter construct which includes a gene for the luciferase protein downstream from a transcription factor binding site. Agonist binding to FOXC2 results in expression of the luciferase gene. Luciferase activity may be quantitatively measured using e.g. luciferase assay reagents that are commercially available from Promega (Madison, WI). Differences in luminescence in the presence versus the absence of a candidate modulator compound are indicative of modulatory activity.

EXAMPLE 14: Expressing profiling and target identification using microarrays

To better understand the role of FOXC2 and thus identify new drug targets, the expression patterns of a large number of genes and ESTs can be monitored using GeneChip® expression microarrays (http://www.affymetrix.com/products/ app_exp.html). Microarrays consist of a highly ordered matrix of thousands of different sequences that can be used to measure DNA and RNA variation in applications that include gene expression profiling, comparative genomics and genotyping (for recent reviews, see e.g.: Harrington et al. (2000) Monitoring gene expression using DNA microarrays. Curr. Opin. Microbiol. 3(3): 285-291; or Dugan et al. (1999) Expression profiling using cDNA microarrays. Nature Genetics supplement 21:10-14).
Briefly. RNAs are extracted from any tissues or cultured cells relevant for the study of FOXC2 and reverse transcribed using a T7-tagged oligo-dT primer to generate doublestranded cDNAs. These cDNAs are then amplified and labeled using In Vitro Transcription (IVT) with T7 RNA polymerase and biotinylated nucleotides. The populations of cRNAs obtained after IVT are purified and fragmented by heat to produce a distribution of RNA fragment sizes from approximately 35 to 200 bases. GeneChip® expression arrays are hybridized with the samples. The arrays are washed and stained. The cartridges are scanned using a confocal scanner and the images are analyzed with the Microarray Suite 4.0 software (Affymetrix).
Using this analysis the role of FOXC2 in specific signaling pathways can be elucidated, and new signaling pathways can be identified. Genes directly or indirectly regulated by FOXC2 can be identified. The analysis will identify genes with previously known function but also novel genes. Gene products functioning in the same pathways as FOXC2 can be considered putative target proteins. Targeting of such proteins would be expected to yield some or all of the desired effects expected from targeting FOXC2 directly.

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Claims

A method for identifying a compound useful for the treatment of obesity, said method comprising the steps

(i) contacting a test compound with the human FOXC2 gene; and

(ii) determining whether said test compound activates the expression of the human FOXC2 gene, such activation being indicative for a compound useful for the treatment of obesity.
A method for identifying a compound useful for the treatment of obesity, said method comprising the steps

(i) contacting a test compound with a polypeptide encoded by the human FOXC2 gene; and

(ii) determining whether said test compound stimulates the biological activities of the said polypeptide, said biological activities comprising reducing total lipid content in a test animaL such stimulation being indicative for a compound useful for the treatment of obesity.